蜀南地区飞仙关组高精度层序地层研究

HIGH-RESOLUTION SEQUENCE STRATIGRAPHY OF THE FEIXIANGUAN FORMATION IN SOUTHERN SICHUAN BASIN

针对四川盆地下三叠统飞仙关组层序地层存在多种不同划分方案,以高精度层序地层学理论与方法为指导,以蜀南地区飞仙关组台地相碎屑岩和碳酸盐岩为研究对象,以野外露头剖面、岩芯、钻井、测井、地震等资料为基础,综合应用岩性突变面、沉积相转换面、沉积物空间堆积样式的变化、早期成岩变化、电测井曲线特征以及地震反射特征等标志,识别出不同级次的11个层序界面,据此将本区飞仙关组划分为2个三级层序(TSQ1和TSQ2)和10个四级层序,其中TSQ1可细分出6个四级层序,TSQ2可再分出4个四级层序,并将其与传统地层单位进行对比:三级层序TSQ1和TSQ2分别对应于飞一段+飞二段地层和飞三段+飞四段地层。通过层序地层对比和层序地层格架的建立,指出这些层序在全区均具有良好的可对比性和等时性,每个层序均具有快速海侵到缓慢海退的特点,均由海侵体系域和高位体系域构成,未发现低位体系域和凝缩段。层序与储层关系的研究表明,四级层序Ⅲ和Ⅷ是台内鲕滩这种有利储集相带的主要发育层位,所形成的滩相鲕粒灰岩储层与高位体系域的向上变浅序列和早期暴露及其所导致的大气淡水淋溶改造有关,平面上集中分布于中东部地区。

To assess the different schemes of sequence stratigraphic division of the Lower Triassic Feixianguan Formation we carried out a high-resolution sequence stratigraphic analysis of the platform facies clastic and carbonate rocks of the Feixianguan Formation in the southern Sichuan Basin outcrop, core, well log, and seismic data. We integrated lithologic discontinuities, sedimentary facies’ changes, stratigraphic stacking pattern diagenetic alternation, electric log, and seismic reflection data, and identified 11 sequence boundaries of different orders. The Feixianguan Formation in this area can be divided into 2 third-order sequences （TSQ1 and TSQ2）and 10 fourth-order sequences, of which 6 are in TSQ1 and 4 are in TSQ2. Correation with traditional lithestratigraphic units shows that, the third-order sequence TSQ1 corresponds to Member 1 and Member 2 whereas the third-order sequence TSQ2 corresponds to Member 3 and Member 4 of the Fexianguan Formation. These sequences can be traced over a large area and are approximately isochronous units each of which is characterized by a rapid transgression followed by a gradual regression. They consist of a transgression and a high-stand system tract, without a lowstand systems thract or a condensed section. The relationship between sequence stratigraphy and reservoir development shows that the fourth-order sequences Ⅲand Ⅷ are the main reseroirss, they are characterized by highstand oolite bank deposits that form shallowing-upward sequences and are often terminated by exposure surfaces.